The present invention relates to a titanium-base hard sintered alloy suitably used as a corrosion- and wear-resistant material for casting molds, pump parts, bearings, mechanical seals, valves, pipes, stirrers, mixers, and blades.
Conventional corrosion- and wear-resistant materials for the above uses are exemplified by the cemented carbides disclosed in Japanese Unexamined Patent Publications Nos. 50-45708 and 1-119639; Stellite, high-chromium cast iron, and SUS440 stainless steel disclosed in Japanese Unexamined Patent Publications Nos. 53-125208 and 60-224732; and Ti--Nb and Ti-6%A1-4%V alloys disclosed in Japanese Unexamined Patent Publication No. 4-83837.
Wear resistance and corrosion resistance are incompatible with each other. Cemented carbides, Stellite, high-chromium cast iron, and hard stainless steel are superior in wear resistance, but not necessarily good in corrosion resistance and, hence, they cannot be used under severe conditions.
Particularly, titanium alloys containing 15 to 30 wt % molybdenum are renowned for having much higher corrosion resistance than pure titanium. However, though titanium alloys are superior in corrosion resistance, they are insufficient in wear resistance.
A titanium alloy with improved wear resistance exists which contains a carbide dispersed therein. It is produced by melting as disclosed in Japanese Unexamined Patent Publication Nos. 2-129330 and 3-285034. Unfortunately, it suffers from disadvantages due to melting. Specifically, its carbide is in the form of coarse grains, which leads to insufficient hardness and wear resistance. In addition, it requires difficult machining to be made into parts having a complex shape after casting.
In order to address the above-mentioned melting problem associated with the titanium alloy, the prevent inventors developed one which is made by powder metallurgy, as disclosed in "Journal of the Japan Society of Powder and Powder Metallurgy", vol 22 No 3. Their development led to a sintered alloy of Ti-30Mo (15.9 vol % Mo) and a sintered alloy of Ti--Mo--TiC having improved wear resistance which is obtained by incorporating the former with TiC in an amount of 10 to 35 wt % (10.1 to 37.2 vol %), as disclosed in Japanese Patent Publication Nos. 51-19403 and 54-19846.
Meanwhile, chemical and machine industries now need titanium-base sintered alloys which, under more severe conditions than before, exhibit good wear resistance as well as high strength without any loss in the corrosion resistance inherent in titanium. This need is not met by the above-mentioned Ti--Mo--TiC sintered alloy because of its insufficient wear resistance and strength. Additionally, the Ti--Mo--TiC sintered alloy does not have sufficient corrosion resistance even though the amount of TiC therein is increased.